Plasticized polyvinyl formal resin



Patented Dec. 13, 1949 UNITED STATES PATENT OFFICE ZJIL SG PLASTICIZED POLYVINYL FORMAL RESIN William E. Richard, Ann Arbor, Mich anignor to Monsanto Chemical Company, St. Louis, Mo,

a corporation of Delaware No Drawing. Application October 13, 1947, Serial No. 179,659

9 Claims. (Cl. 260-318) l 2 This invention relates to polyvinyl formaldel'mmple 11 hyde acetal resin compositions. More particularly, this invention relates to plasticized polyvinyl formals.

The problem of providing suitable materials for plasticizing polyvinyl formals has proved to be particularly difllcult. Thus, in contrast to other acetal resins such as polyvinyl butyrals, only a limited group of compounds have proved to be suitable. One of the chief difllculties has been lack of compatibility of compounds which are successful plasticizers for other high molecular weight materials, as for example, polyvinyl butyrals. Another difliculty has been the tendency of such materials as are sufliciently compatible with polyvinyl formal to volatilize from the plasticized resin at elevated temperatures.

It is an object of this invention to provide plasticlzed polyvinyl formal resin compositions. A particular object of this invention is to provide plasticized polyvinyl formals of improved stability at elevated temperatures.

These and other objects are attained according to this invention by incorporating in polyvinyl formal an alkyl ester of a phthalic acid from the group 3-nitro and 4-nitro phthalic acids wherein the alkyl groups contain 1-4 carbon atoms. Thus, it has been found that the above described esters have a high degree of compatibility with polyvinyl formal resin and at the same time have a greatly decreased rate of volatilize.- tion from the polyvinyl formal compositions.

The following examples are given in illustration of the present invention, but are not to be considered as limitative thereof. Where parts are mentioned, they are parts by weight.

The polyvinyl formal used in the examples is made by simultaneously hydrolyzing and reacting with formaldehyde a polyvinyl acetate of such a viscosity that a one-molar benzene solution thereof has a viscosity of centipoises at C. The reaction is carried out under such conditions that the product contains '7-9% hydroxyl groups 7 by weight calculated as polyvinyl alcohol, 9-l3% acetate groups by weight, calculated as polyvinyl acetate and the balance substantially formaldehyde-acetal.

Example I Example 11 is repeated except that 25 parts of the ester plasticizer are used in place of parts.

A sheet pressed from the product in the same manner as in Example I is light colored, transparent and flexible although somewhat stiffer than the product of Examples I and II.

In place of the diethyl and dibutyl esters of 4- nitro phthalic acid, the dimethyl or dipropyl esters may be used with generally similar results. Likewise, the dimethyl, diethyl, dipropyl and dibutyl esters of 3-nitro phthalic acid may be substituted for the esters in the examples to yield plasticized polyvinyl formal resin products of generally similar properties.

In contrast to the alkyl nitro phthalates of the invention, the use of the corresponding alkyl phthalates free from nitro groups gives greatly inferior results. Not only do the esters of the invention possess greater compatibility with polyvinyl formals, but in particular the plasticizers of the invention show unexpectedly better retentivity in the compositions as compared with the corresponding dialkyl phthalates of the prior art. This superiority of the compositions of the invention is illustrated by the results set forth in Table A wherein the percentage weight loss for films made from the compositions of the invention is contrasted with the percentage weight loss when the usual alkyl phthalates are used. In each case, 100 parts of plasticizer is incorporated in 100 parts of polyvinyl formal, a sheet 0.020 inch in thickness is made therefrom and the weight loss is determined on heating for 5 hours at C.

Among the other advantages flowing from the use of the plasticizers oi the invention, it is noted that films made from compositions containing equal parts of polyvinyl formal and diethyl phthalate are extremely tacky, whereas, as is pointed out above, the compositions of the invention in the same proportions are free from tackiness. It is also noted that when dibutyl phthalate is mixed with polyvinyl formal in equal proportions, the resulting compositions strongly exude plasticizer, indicating that the point of compatibility has been greatly exceeded, whereas the corresponding composition of the invention as illustrated by Example II is only slightly above the point of maximum compatibility.

As pointed out above, the alkyl portion of the esters used in the compositions of the invention 4 may contain l-4 carbon atoms. While the illustrative examples show esters in which both alkyl groups are the same, corresponding esters may be used in which the alkyl groups differ, provided neither contains more than four carbon atoms.

The amount of ester to be incorporated in the polyvinyl formal depends on a number of factors, for example, the intended use for the plastlcized resin as well as the presence or absence The upper limit of comof other plasticizers. patability of the plasticizers of the invention depends not only on the presence or absence of other plasticizers, but upon the nature of the alkyl portion of the molecule, i. e., the longer the alkyl chain the lower the compatability.

Examples of plasticizers which may be used in conjunction with the plasticizers of the invention include diacetin, diethyl phthalatc, dibutyl tartrate, triethyl citrate, etc. For example, 25-50 parts of one or more of these plasticizers may be used in conjunction with 25-50 parts of one or more plasticizers of the invention in 100 parts of polyvinyl formal.

While, as indicated above, the amount of plasticizer depends, at least in part, on the intended use, it is desirable to have present at least 25 parts of plasticizer for every 100 parts of acetal resin and it is expected that the esters of the invention will be generally used in compatible amounts within the range 25-150 parts for every 100 parts of polyvinyl formal. A more preferred range is 40-100 parts of an ester of the invention for every 100 parts of polyvinyl formal.

As is known to those skilled in the art, the composition of polyvinyl formal resins may be varied to a wide extent. This is indicated by U. S. reissue 20,430 to Morrison et al. For example, the acetal resin may be made from polyvinyl acetate or other polyvinyl ester having widely varying viscosities. Thus, in the case of polyvinyl acetate, the degree of polymerization may be such that a one-molar benzene solution has a viscosity of 5-500 centipoises at C. Corresponding variation in the degree of polymerization of other polyvinyl esters is permissible. As indicated in the Morrison et a1. patent referred to above, polyvinyl formals may vary widely with respect to the'relative proportion of hydroxyl.

"forth above, the preferred ester groups are derived from acetic acid.

It is to be understood that the above description is given by way of illustration only, and not of limitation, and that deviations are possible within the spirit of the invention.

What is claimed is:

l. A composition having improved plasticizer retentivity at elevated temperatures comprising a polyvinyl formal resin plasticized with a dialkyl ester of a phthalic acid from the group consisting of 3-nitro phthalic acid and *i-nitro phthalic acid in which the alkyl groups contain less than '5 carbon atoms. 2. A composition as defined in claim .1 in which the ester is an ester of 3-nitro phthalic acid.

3. A composition as defined in claim 1 in which the ester is an ester of 4-nitro phthalic acid.

4. A composition as defined in claim 3 in which the alkyl groups are ethyl groups.

.a compatible amount of the ester is used, but

said amount is at least 25 parts for every parts of polyvinyl formal.

8. A composition as defined in claim 1 in which the ester is an ester of 4-nitro phthalic acid and in which the alkyl groups are butyl groups.

9. A composition as defined in claim 8 in which the amount of ester does not exceed its compat-' ibility with the acetal resins, but is at least 25 parts for every 100 parts of acetal resin.

WILLIAM R. RICHARD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name- Date 2,072,739 Dykstra Mar. 2, 1937 FOREIGN PATENTS Number Country Date 509,596 Great Britain July 17, 1939 

